1. Field of the Invention
The present invention relates generally to the field of fine powder processing, and particularly to the metered transport of fine powders. More particularly, the present invention relates to systems, apparatus and methods for filling receptacles with unit dosages of non-flowable but dispersible fine powdered medicaments, particularly for subsequent inhalation by a patient.
Effective delivery to a patient is a critical aspect of any successful drug therapy. Various routes of delivery exist, and each has its own advantages and disadvantages. Oral drug delivery of tablets, capsules, elixirs, and the like, is perhaps the most convenient method, but many drugs are have disagreeable flavors, and the size of the tablets makes them difficult to swallow. Moreover, such medicaments are often degraded in the digestive tract before they can be absorbed. Such degradation is a particular problem with modern protein drugs which are rapidly degraded by proteolytic enzymes in the digestive tract. Subcutaneous injection is frequently an effective route for systemic drug delivery, including the delivery of proteins, but enjoys a low patient acceptance and produces sharp waste items, e.g. needles, which are difficult to dispose. Since the need to inject drugs on a frequent schedule such as insulin one or more times a day, can be a source of poor patient compliance, a variety of alternative routes of administration have been developed, including transdermal, intranasal, intrarectal, intravaginal, and pulmonary delivery.
Of particular interest to the present invention are pulmonary drug delivery procedures which rely on inhalation of a drug dispersion or aerosol by the patient so that the active drug within the dispersion can reach the distal (alveolar) regions of the lung. It has been found that certain drugs are readily absorbed through the alveolar region directly into blood circulation. Pulmonary delivery is particularly promising for the delivery of proteins and polypeptides which are difficult to deliver by other routes of administration. Such pulmonary delivery can be effective both for systemic delivery and for localized delivery to treat diseases of the lungs.
Pulmonary drug delivery (including both systemic and local) can itself be achieved by different approaches, including liquid nebulizers, metered dose inhalers (MDI's) and dry powder dispersion devices. Dry powder dispersion devices are particularly promising for delivering protein and polypeptide drugs which may be readily formulated as dry powders. Many otherwise labile proteins and polypeptides may be stably stored as lyophilized or spray-dried powders by themselves or in combination with suitable powder carriers. A further advantage is that dry powders have a much higher concentration that medicaments in liquid form.
The ability to deliver proteins and polypeptides as dry powders, however, is problematic in certain respects. The dosage of many protein and polypeptide drugs is often critical so it is necessary that any dry powder delivery system be able to accurately, precisely and repeatably deliver the intended amount of drug. Moreover, many proteins and polypeptides are quite expensive, typically being many times more costly than conventional drugs on a per-dose basis. Thus, the ability to efficiently deliver the dry powders to the target region of the lung with a minimal loss of drug is critical.
For some applications, fine powder medicaments are supplied to dry powder dispersion devices in small unit dose receptacles, often having a puncturable lid or other access surface (commonly referred to as blister packs). For example, the dispersion device described in, U.S. Pat. No. 5,785,049, the disclosure of which is herein incorporated by reference, is constructed to receive such a receptacle. Upon placement of the receptacle in the device, a "transjector" assembly having a feed tube is penetrated through the lid of the receptacle to provide access to the powdered medicament therein. The transjector assembly also creates vent holes in the lid to allow the flow of air through the receptacle to entrain and evacuate the medicament. Driving this process is a high velocity air stream which is flowed past a portion of the tube, such as an outlet end, entraining air and thereby drawing powder from the receptacle, through the tube, and into the flowing air stream to form an aerosol for inhalation by the patient. The high velocity air stream transports the powder from the receptacle in a partially de-agglomerated form, and the final complete de-agglomeration takes place in the mixing volume just downstream of the high velocity air inlets.
Of particular interest to the present invention are the physical characteristics of poorly flowing powders. Poorly flowing powders are those powders having physical characteristics, such as flowability, which are dominated by cohesive forces between the individual units or particles (hereinafter "individual particles") which constitute the powder. In such cases, the powder does not flow well because the individual particles cannot easily move independently with respect to each other, but instead move as clumps of many particles. When such powders are subjected to low forces, the powder will tend not to flow at all. However, as the forces acting upon the powder is increased to exceed the forces of cohesion, the powder will move in large agglomerated "chunks" of the individual particles. When the powder comes to rest, the large agglomerations remain, resulting in a non-uniform powder density due to voids and low density areas between the large agglomerations and areas of local compression.
This type of behavior tends to increase as the size of the individual particles becomes smaller. This is most likely because, as the particles become smaller, the cohesive forces, such as Van Der Waals, electrostatic, friction, and other forces, become large with respect to the gravitational and inertial forces which may be applied to the individual particles due to their small mass. This is relevant to the present invention since gravity and inertial forces produced by acceleration, as well as other effected motivators, are commonly used to process, move and meter powders.
For example, when metering the fine powders prior to placement in the unit dose receptacle, the powder often agglomerates inconsistently, creating voids and excessive density variation, thereby reducing the accuracy of the volumetric metering processes which are commonly used to meter in high throughput production. Such inconsistent agglomeration is further undesirable in that the powder agglomerates need to be broken down to the individual particles, i.e. made to be dispersible, for pulmonary delivery. Such de-agglomeration often occurs in dispersion devices by shear forces created by the air stream used to extract the medicament from the unit dose receptacle or other containment, or by other mechanical energy transfer mechanisms (e.g., ultrasonic, fan/impeller, and the like). However, if the small powder agglomerates are too compacted, the shear forces provided by the air stream or other dispersing mechanisms will be insufficient to effectively disperse the medicament to the individual particles.
Some attempts to prevent agglomeration of the individual particles are to create blends of multi-phase powders (typically a carrier or diluent) where larger particles (sometimes of multiple size ranges), e.g. approximately 50 .mu.m, are combined with smaller drug particles, e.g. 1 .mu.m to 5 .mu.m. In this case, the smaller particles attach to the larger particles so that under processing and filling the powder will have the characteristics of a 50 .mu.m powder. Such a powder is able to more easily flow and meter. One disadvantage of such a powder, however, is that removal of the smaller particles from the larger particles is difficult, and the resulting powder formulation is made up largely of the bulky flowing agent component which can end up in the device, or the patient's throat.
Current methods for filling unit dose receptacles with powdered medicaments include a direct pouring method where a granular powder is directly poured via gravity (sometimes in combination with stirring or "bulk" agitation) into a metering chamber. When the chamber is filled to the desired level, the medicament is then expelled from the chamber and into the receptacle. In such a direct pouring process, variations in density can occur in the metering chamber, thereby reducing the effectiveness of the metering chamber in accurately measuring a unit dose amount of the medicament. Moreover, the powder is in a granular state which can be undesirable for many applications.
Some attempts have been made to minimize density variations by compacting the powder within, or prior to depositing it in the metering chamber. However, such compaction is undesirable, especially for powders made up of only fine particles, in that it decreases the dispersibility of the powder, i.e. reduces the chance for the compacted powder to be broken down to the individual particles during pulmonary delivery with a dispersion device.
It would therefore be desirable to provide systems and methods for the processing of fine powders which would overcome or greatly reduce these and other problems. Such systems and methods should allow for accurate and precise metering of the fine powder when divided into unit doses for placement in unit dose receptacles, particularly for low mass fills. The systems and methods should further ensure that the fine powder remains sufficiently dispersible during processing so that the fine powder may be used with existing inhalation devices which require the powder to be broken down to the individual particles before pulmonary delivery. Further, the systems and methods should provide for the rapid processing of the fine powders so that large numbers of unit dose receptacles can rapidly be filled with unit dosages of fine powder medicaments in order to reduce cost.
2. Description of the Background Art
U.S. Pat. No. 4,640,322 describes a machine which applies sub-atmospheric pressure through a filter to pull material directly from a hopper and laterally into a non-rotatable chamber.
U.S. Pat. No. 2,540,059 describes a powder filling apparatus having a wire loop stirrer for stirring powder in a hopper before directly pouring the powder into a metering chamber by gravity.
German patent DE 3607187 describes a mechanism for the metered transport of fine particles.
Product brochure, "E-1300 Powder Filler" describes a powder filler available from Perry Industries, Corona, Calif.
U.S. Pat. No. 3,874,431 describes a machine for filling capsules with powder. The machine employs coring tubes that are held on a rotatable turret.
British Patent No. 1,420,364 describes a membrane assembly for use in a metering cavity employed to measure quantities of dry powders.
British Patent No. 1,309,424 describes a powder filling apparatus having a measuring chamber with a piston head used to create a negative pressure in the chamber.
Canadian Patent No. 949,786 describes a powder filling machine having measuring chambers that are dipped into the powder. A vacuum is then employed to fill the chamber with powder.